$\DeclareMathOperator{\p}{Pr}$ $\DeclareMathOperator{\P}{Pr}$ $\DeclareMathOperator{\c}{^C}$ $\DeclareMathOperator{\or}{ or}$ $\DeclareMathOperator{\and}{ and}$ $\DeclareMathOperator{\var}{Var}$ $\DeclareMathOperator{\E}{E}$ $\DeclareMathOperator{\std}{Std}$ $\DeclareMathOperator{\Ber}{Bern}$ $\DeclareMathOperator{\Bin}{Bin}$ $\DeclareMathOperator{\Poi}{Poi}$ $\DeclareMathOperator{\Uni}{Uni}$ $\DeclareMathOperator{\Exp}{Exp}$ $\DeclareMathOperator{\N}{N}$ $\DeclareMathOperator{\R}{\mathbb{R}}$ $\newcommand{\d}{\, d}$

CS109 Midterm
Tuesday July 23rd, 7pm

Logistics

The CS109 midterm is 2 hours long. You will receive the exam printed out and write your answers in the space below each question on each page (that is where we will look when grading).

The exam is closed book and closed calculators/computers. You are, however, allowed to bring 5 pages (front and back) of notes in the exam, formatted in any way you like, printed or handwritten.

Make sure to practice before the exam.

Where to Go

Building 300, room 300. Building 300 is part of main quad (the older buildings in the center of campus).

Alternative Arrangements

If you can not make the CS109 midterm because of an academic conflict (such as having another midterm) we will help you schedule an alternative. Please reach out to us over email (cs109@cs.stanford.edu) at least one week before the exam.

Coverage

The midterm puts special emphasis on the material from the first three problem sets and the first four sections. This includes material in lecture up to and including class on Friday, July 19th. In the reader this corresponds to Part 1 and Part 2, and Part 3 up through the "inference" section.

Answer Format

You are going to be solving probability questions by hand. To that extent we are not interested in numeric answers, but rather in formulaic answers. It is fine for your answers to include summations, products, factorials, exponentials, and combinations, unless the question specifically asks for a numeric quantity or closed form. Where numeric answers are required, the use of fractions is fine. You must show your work. Any explanation you provide of how you obtained your answer can potentially allow us to give you partial credit for a problem. For example, describe the distributions and parameter values you used, where appropriate.

What about the Phi table? We are not going to make you look up values from a phi table. Instead you can leave your answer in terms of phi (the CDF of the standard normal). For example $\Phi(\frac{3}{4})$ is a fine final answer. This was not the case in the past so you will see questions which ask for a numeric answer in the practice exams.

Essential Practice

Below are practice exams from previous offerings of CS109. We recommend taking at least one practice exam, under realistic time constraints, before taking the real thing. Note: The TAs are less familiar with problems from the practice exams, compared to psets (there are far too many for them to prep them all). When asking about practice exam problems on Ed or in office hours, please be ready to give the full context, and be aware that the TA might not be able to prioritize them. This is especially true more than a week before the exam.

Extra Practice

You can do it!